Adjustable mounting device for electrostatic copier developer magazine

ABSTRACT

A mounting apparatus for the developer magazine of an electrostatic copier which enables the developer brushxerographically sensitive element spacing to be varied across the width of the brush. Two independently adjustable eccentric cams bear upon the rear of the developer magazine to determine the spacing. A spring-loaded anchor bar is slidably received on spaced guide members secured to the front of the developer magazine to provide a rearward thrust for maintaining the spacing constant independently of dimensional changes in the copier frame units.

2,061,692 11/1936 Bagley United States Patent lnventor Ray S. RichmondPlacitas, N. Mex.

Appl, No. 21,609

Filed Mar. 23, 1970 Patented Dec. 21, 1971 Assignee The Singer CompanyNew York, N.Y.

ADJUSTABLE MOUNTING DEVICE FOR ELECTROSTATIC COPIER DEVELOPER MAGAZINE10 Claims, 3 Drawing Figs.

US. Cl .Q 118/637,

Int. Cl G03g 13/00 Field of Search 118/637, 637LX;117/175;19/135;175/133;250/49.5

References Cited UNITED STATES PATENTS 2,153,118 Harris 19/135 2,807,2339/1957 Fitch 118/637 2,912,586 11/1959 Gundlach 250/495 2,943,908 7/1960Hanna s 346/74 3,063,859 11/1962 l-leckscher ll7/l7.5

Primary Examiner-Mervin Stein Assistant Examiner-Leo MillsteinAttorneys-Patrick J. SchlesingenCharles R. Lepchinsky,

Warren P. Kujawa and Jay M. Cantor ABSTRACT: A mounting apparatus forthe developer magazine of an electrostatic copier which enables thedeveloper brush-xerographically sensitive element spacing to be variedacross the width of the brush. Two independently adjustable eccentriccams bear upon the rear of the developer magazine to determine thespacing. A spring-loaded anchor bar is slidably received on spaced guidemembers secured to the front of the developer magazine to provide arearward thrust for maintaining the spacing constant independently ofdimensional changes in the copier frame units.

ill

PATENTED W321 B7! SHEET 1 OF 2 RAY S. RICHMOND INVENT BACKGROUND OF THEINVENTION l. Field of Invention This invention relates to dryelectrostatic copiers having a developer magazine with the brush fordepositing toner particles on the surface of a xerographically sensitiveelement. More particularly, the invention relates to the mountingapparatus formed in such copiers for mounting the developer magazineadjacent the xerographically sensitive element.

2. Description of the Prior Art Electrostatic copiers are known whichemploy a xerographically sensitive element, such as a zinc oxide coatedpaper web, for developing a visible image of a document to bereproduced. in such a device, a latent image is first formed on thesurface of the web by depositing electrostatic charges thereon andselectively dissipating certain charges to form a charge patterncorresponding to the original document. Next, a dry visible toner powderis distributed onto the charged surface of the web, customarily by meansof a magnetic brush which rotates about an axis parallel to thetransverse direction of the web surface. By the mechanism oftriboelectric attraction, the distributed toner particles adhere to theelectrostatic charges on the web surface, thereby rendering the latentimage visible. This visible image is then ordinarily fixed by heatinguntil the toner particles melt and fuse with the web surface.Alternatively, the visible powder image may be transferred from the websurface to a second surface, such as a sheet of paper, and fixed thereonby heating.

While there are many determining factors which influence the quality ofthe developed image, given a substantially uniform surface chargedistribution the single most significant factor determining imagequality is the degree of uniformity with which the toner powder isdistributed on the surface of the web. Many copiers employ magneticbrush development for distributing the toner. In a typical arrangement,the brush consists of a magnetized core member, such as a permanentlymagnetized cylinder, and magnetic particles, such as iron filings, whichare attracted by magnetic forces to the surface of the core, formingbrushlike tufts or streamers on the surface thereof. The brush isordinarily encased in a developer magazine which also carries componentsfor mixing the toner powder with the magnetic particles. In operation,the toner powder is introduced into the mixing portion of the developermagazine where it is thoroughly intermixed with the magnetic particles.During mixing, particles of toner are attracted by and adhere to themagnetic particles by triboelectric forces therebetween. The tonerbearing magnetic particles are then swept over the charged web surfaceby the brush core. Those toner particles which encounter electrostaticcharges are removed from their magnetic carriers by the force ofelectrostatic attraction therebetween and remain behind on the websurface. The magnetic carrier particles are then returned by the brushcore to the mixing portion of 'the developer magazine where they acquirefresh toner particles, and the process is repeated.

It has been found that maximum utilization of a zerographicallysensitive web is realizable if the web is arranged vertically in theworking region, defined by the charging and developing stations in thosecopiers which fix the visible image on the web, and defined by thecharging and transfer stations in those copiers which fix the visibleimage after transfer to a second surface. However, this arrangementintroduces a critical parameter in the design of the developing station:namely, the separation distance between the surface of the charged weband the surface of the magnetic brush core. If this distance is toogreat, no toner particles will approach close enough to the surfacecharges on the web to be attracted thereto and the result will be anundeveloped, invisible image. On the other hand, if this distance is toosmall, the surface friction between the magnetic particles and the websurface will cause great quantities of the magnetic particles to beseparated from the brush core, causing partial dissipation of the chargedistribution (since the magnetic particles are also electricallyconductive), fouling of machine components located below the developingstation and an excessive deposition of toner particles onto the websurface which results in an exceedingly dark and sometimes completelyblack developed image. In between these two extremes lies an optimumspacing which varies according to the desired image contrast, themagnetic field strength at the brush core surface, the permeability andlinear dimensions of the magnetic particles, the strength of thetriboelectric forces between the toner and magnetic particles, and otherfactors. Once achieved, this optimum spacing must be rigidly maintainedto ensure good copy quality.

A further complicating factor tending to compound the web-core surfacespacing problem resides in the requirement that the optimum spacing,once determined, must be maintained substantially constant across theentire width of the web surface. Stated otherwise, this spacing must notvary appreciably along a path traced parallel to the transversedirection of the web surface. In addition, any mechanism incorporatedinto the copier apparatus for obtaining and maintaining this optimumspacing must be extremely simple in order that it be easily adjustablein the operational environment of the copier and to avoid theunnecessary introduction of additional parts which necessitates furtherexpense and increases the probability of operational failure of thedevice. Past efforts to devise such a simple mechanism have, at best,met with limited success.

Many copiers utilize two separate subassemblies for mounting the variouselectrical and mechanical components. Customarily,the main subassemblycarries the main drive frame, the web supply system, and other copiercomponents all mounted within a first frame unit, while the secondsubassembly carries the original document feed mechanism, the developermagazine, the corona stations and the fusing station used to fix thedeveloped image, all mounted within a second frame unit. These two frameunits are ordinarily positioned together in abutting relationship as arigid unit, and in more advanced machines the connecting members servingto secure these frame units together are designed to be readilydisconnected so that the two units can be easily and quickly separatedto provide access to. the interior of the copier when servicing isrequired. This convenient feature, however, creates a severe problemrelating to the constancy of the webcore spacing. Due to the heatgenerated by the fusing station during the fixing step of the imagedevelopment process, abutting portions of the two frame units expand.Since the developer unit ordinarily is rigidly mounted in the secondframe unit, this expansion severely alters the web-core spacing and thusthe copy quality in the manner discussed above. Moreover, during thoseperiods when the fuser is deactuated, the above-mentioned portionscontract upon cooling. Consequently, with prolonged use the resultingalternate expansion and contraction of the affected frame unit portionseventually results in a permanent misalignment of the web-corerelationship which can only be rectified by costly, time-consumingrepairs or by replacing the entire second subassembly.

SUMMARY OF THE INVENTION The invention disclosed herein comprises amounting apparatus for the developer magazine of an electrostatic copierwhich enables a quick, simple, and precise alignment of the web-corespacing without requiring any separation of the two subassemblies whichcarry the major components of the machine. More particularly, thedisclosed invention resides in an eccentric cam assembly which isreleasably secured to a transverse shaft to provide a pair of abutmentsurfaces for the brush end of the developer magazine, and which can beeasily adjusted to vary the web-core spacing. Additionally, thedisclosed invention includes a mechanism which coacts with the spacingadjustment means for maintaining the selected webcore spacing constantindependently of dimensional changes in the copier frame unit. Moreparticularly, this portion of the novel mounting apparatus comprises aspring-loaded anchor bar fixed to a remote portion of the second frameunit and slidably received on spaced guide members secured to the frontof the developer magazine to provide a rearward thrust for maintainingthe web-core spacing constant over a wide range of such dimensionalchanges.

For a fuller understanding of the nature and advantages of theinvention, reference should be had to the following detaileddescription, taken in conjunction with the accom panying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspectiveillustrating a preferred embodiment of the invention;

FIG. 2 is a plan view partially in section of the FIG. 1 embodiment',and

FIG. 3 is a detailed view of a portion of the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to FIG. 1, a portionof an electrostatic copier is shown which illustrates the preferredembodiment of the invention. Situated on a copier base are a pair offrame units 12 and 13. Main frame unit 12 includes a left sideplate 14and a right sideplate 15, while front frame unit 13 includes a leftsideplate 16 and a right sideplate 17.

Extending transversely of main frame unit 12 is a central support shaft20. Shaft 20 is journaled at a first end into an aperture 21 insideplate 15, and is rotatably supported at an opposite end by acylindrical support member 22 which is positioned in a slot 23 insideplate 14. Fixed to shaft 20 adjacent sideplate is an eccentric cam24. A first adjusting knob 25 is secured to the opposite end of shaft sothat rotation of knob results in rotation of eccentric cam 24. Adjacentknob 25 is a second adjusting knob 26 which is secured to an eccentriccam 27. Cam 27 is rotatably received on shaft 20 between knob 26 andsupport member 22.

Located between sideplates l4 and 15 of main frame unit 12 is a websupport cylinder 30 which is mounted on shaft 20 for free rotationthereabout. Web support cylinder 30 provides a rotatable support surfacefor the back of a photoconductive web 32. Web 32 is passed over cylinder30 in the direction indicated by the arrow by a drive mechanism (notshown) carried by main frame unit 12. Main frame unit 12 carries othercopier components which are known to those skilled in the art and whichhave not been illustrated for purposes of clarity.

A developer magazine 33 having an inlet 34 for the introduction of tonerto the interior thereof is slidably supported at each side by a pair ofL-shaped channel members 36, 37 which are secured to sideplates 14, 15by any suitable means, such as welding. Although shown attached tosideplates 14, 15 of main frame unit 12, channel members 36, 37 may beattached to any of the sideplates 14-17 in any convenient fashion whichprovides a support for developer magazine 33.

As shown in FIG. 2, developer magazine 33 contains a cylin dricalmagnetic core 40 comprising a plurality of ferrite discs 41concentrically mounted on a metal rod 42. Rod 42 is rotatably receivedby two bearings 43, 44 the latter visible in FIG. 1) mounted inapertured sidewalls 45, 46 and preferably made of bronze. A gear 47 ismounted on the driven end of rod 42 and is arranged to mesh with theteeth of gear 48, which is also engaged with gear 49, Gears 43 and 19are secured to bearing-mounted mixing augers (not shown) which arearranged in a known manner to transport toner from inlet 34 to theinterior region adjacent core 40 and to mix the toner with iron filingscontained in magazine 33. Gear 47 is driven by a spur gear (not shown)mounted on main frame unit 12 and driven in a known manner.

A real wall portion 50 of developer magazine 33 is cutaway as shown toprovide an open space between the surface of web 32 and core 40. Asdiscussed above, when magnetic core 10 is rotated by gear 417,toner-bearing magnetic particles are brushed across the surface ofphotoconductive web 32 along the entire width thereof in the spaceprovided by the cutaway portion of rear wall 50.

Extending forwardly of developer magazine 33 are a pair of guide members51, 52 which are fixed to the front portion of magazine 33. Disposedabout guide members 51, 52 are compressively mounted springs 53, 54. Ananchor bar 55 is adjustably secured to sideplates 16, 17 of front frameunit 13 by screws 56 which pass through slots 57. Anchor bar 55 has apair of apertures which slidably receive guide members 51, 52. A pair ofkeepers 53, 59 are mounted on guide members 51. 52 as shown to providestops for presenting removal of anchor bar 55 from guide members 51, 52.As is evident to those skilled in the art, front frame unit 13 carriesother copier components than developer magazine 33, such as the originaldocument and copy paper feed mechanisms, and the fusing station, withthe latter ordinarily located above developer magazine 33 adjacent thetop surface of the copier. These components have been omitted forpurposes of clarity in illustrating the preferred embodiment of theinvention. In addi tion, front frame unit 13 is releasably secured tomain frame unit 12 in any suitable manner known to those skilled in theart; e.g., sideplates 14, 15 may be provided with inwardly projectingdowel pins at their upper front portions and sideplates 16, 17 may beprovided at their upper rear portions with pivotable hooks which areengageable with the dowel pins. Other arrangements will occur to thoseskilled in the art.

FIG. 2 illustrates in more detailed fashion the components of thepreferred embodiment which comprise the web-core spacing means and theapparatus for maintaining this spacing constant independent ofdimensional changes in the copier frame units. As shown in FIG. 2, in anassembled apparatus, developer magazine 33 is urged rearwardly bysprings 53, 54 acting on the front of magazine 33 and anchored by fixedanchor bar 55. Front surfaces 61, 62 of sidewalls 46, 45 of magazine 33bear against the contoured surfaces of eccentric earns 27, 241,respectively. Accordingly, the linear distance between front surfaces61, 62 and the axis of rod 20 will vary according to the angularposition of cams 27, 24, respectively. Since the position of the surfaceof web 32 is fixed with reference to the axis of rod 20, and since theposition of core member 40 is fixed with reference to front surfaces 60,61 by bushings 14, d3, respectively, the linear distance between thesurface of web 32 and core 40 may be varied by adjusting the angularposition of cams 27 and 24. Further, this linear distance between theweb-core surface may be adjusted so as to be uniform across the entirewidth of web 32, or skewed, as desired, by independently varying theangular position of eccentric cams 27, 24. Thus, as viewed in FIG. 2,the web-core spacing at the right side of web 32 may be adjusted to beless than, equal to, or greater than the spacing at the left side of web32, by individually rotating knobs 25, 26.

The adjustable web-core spacing assembly will now be described in detailwith reference to FIG. 2. As viewed in FIG. 2, the right end of centralsupport shaft 20 is rotatably journaled in right sideplate 15. Spacedfrom this journal is eccentric cam 24, which is provided with an axialcylindrical bore and a radial bore which is threaded to receive a lockscrew Ml. Adjacent the left end of support shaft 20 is cylindricalsupport member 22 having a threaded radial bore provided with a lockscrew 65 and which is rigidly fixed to the front of left sideplate 14 bynut 66. Support shaftZO is rotatably received by support member 22 andmay be locked thereto by tightening lock screw 65. A spacing collar 67is secured to support shaft 20 on the inner side of nut 66 to provide anadjustable amount of left end play for support shaft 20.

Mounted on support shaft 20 to the immediate left of support member 22is eccentric cam 27, similar to eccentric cam 24, having an axialcylindrical bore and a radial bore which is threaded to receive a lockscrew 69. Fixed to the left end of eccentric cam 27 is knob 26 having acylindrical collar portion 70. To the immediate left of knob 26is-knob'25, having a cylindrical collar portion 71, and which is fixedto the left end of support shaft 20 by, lock screw 72 (see FIG. 3).

symmetrically mounted on support shaft 20 with respect to the innersurfaces of side plate l4, are two support collars 75, 76 having lockscrews 77, 78. Web support cylinder 30 is coupled to support collars 75,76 by any suitable low-friction means known to those skilled in the art,such as needle bearings, so as to be freely rotatable with respect tosupport shaft 20. As mentioned above, web support cylinder 30 provides afreely rotatable support for the back of photoconductive web 32.

The adjustable web-core spacing assembly is assembled as follows:central support shaft is passed through the components interior tosideplates 14, 15, i.e., nut 66, spacing collar 67, support collars 75,76 and web support cylinder 30, and eccentric cam 24. Next, supportmember 22 is slipped onto shaft 20 and positioned in slot 23 (seeFIG. 1) after which the right end of shaft 20 is journaled into aperture21 of sideplate 15. Support member 22 is next secured in slot 23 bytightening nut 66, care being taken to align support shaft 20 normal tosideplates 14, 15.

With reference to FIG. 3, the eccentric cam 27-knob 26 assembly is nextfitted onto shaft 20, after which knob 25 is fitted onto shaft 20 andsecured thereto by tightening lock screw 72. Spacing collar 67 is thenpositioned on shaft 20 to provide the desired amount of left end playand fixed to shaft 20 by tightening lock screw 68. Following this,support collars 75, 76 and web support cylinder are centered on supportshaft 20 and locked in place by tightening lock screws 77, 78. Theapparatus is now ready for installation of developer magazine 33. I

The first set step in the installation of developer magazine 33 is thealignment of the angular positions of eccentric cams 27, 24. This isaccomplished by rotating either one of the two knobs 25, 26 whilesteadying the other until the angular positions of eccentric cams 27, 24are approximately equal. Eccentric cam 27 is then locked to shaft 20 by.tightening lock screw 69, thereby interlocking the two eccentric cams.The interlocked eccentric cams 27, 24 are then rotated to an arbitraryintermediate angular position by rotating knobs 25, 26, after which theyare locked against rotation by securing lock screw 65 of support member22.

Following this, developer magazine 33 is placed onto channel members 36,37 and slide rearwardly until front surfaces 61, 62 bear against thesurfaces of eccentric cams 27, 24. While maintaining this surfacecontact, springs 53, 54 are next compressed by forcing anchor bar 55rearwardly. Installation of developer magazine 33 is then completed bytightening screws 56 to secure anchor bar 55 in place. The copier is nowready for adjustment of the web 32-magnetic core 40 spacing.

The copier is actuated in a known manner to provide a test electrostaticimage on the surface of web 32 which is uniform across the widththereof. Lock screws 65 and 69 are then loosened so that eccentric cams27 and 24 may be independently rotated. The test operator then adjuststhe angular positions of eccentric cams 27 and 24 by rotating knobs 25and 26 until a visible image is produced on the emerging surface of web32 which is uniform across the entire width of web 32. During theadjustment process, compressed springs 53, 54.ensure that the frontsurfaces 61, 62 of developer magazine 33 are maintained in contact withthe surfaces of eccentric cams 27, 24 so that the web 32-core 40 spacingvaries smoothly until the uniform image is obtained. Once the uniformimage is thus obtained, eccentric cams 27 and 24 are interlocked bytightening lock screw 69 of eccentric cam 27. Following this, eccentriccams 27, 24 are rotated in synchronism to obtain the desired imageintensity, and thus the optimum web 32-core 40 spacing. During thisadjustment, the interlock provided by tightened lock screw 69 ofeccentric cam 27 ensures that the predetermined transverse imageuniformity previously obtained is not disturbed. When the desired imageintensity is obtained, eccentric cams 27, 24 are locked against rotationby tightening lock screw 65 of support member 22. With the optimum web32-core 40 spacing now determined, and eccentric cams 27, 24 lockedagainst rotation, the copier is now ready for use.

As mentioned above, the fusing station is ordinarily located above theweb 32-core 40 region. With prolonged copier use, the heat generated bythe fusing station causes expansion of adjacent portions of sideplates14, 15 of main frame unit 12 and sideplates l6, 17 of front frame unit13. In ordinary copiers not provided with the disclosed invention, thisexpansion can be communicated to developer magazine 33 resulting inalteration of the critical web 32-core 40 spacing, which must be held totolerances as close as $0.010 inch in some copiers. As also noted above,alteration of the web-core spacing can have an extremely adverse affecton the quality of the visible image developed on the surface of web 32.

In the disclosed invention, however, the web 32-core 40 spacing ismaintained constant independently of any expansion of portions of frameunits 12, 13, which may be adjacent to the copier fusing station. As canbe seen from FIGS. 1 and 2, the web 32-core 40 spacing is determined bythe angular positions of eccentric cams 27, 24 which bear upon frontsurfaces 61, 62 of slidably mounted developer magazine 33. So long asfront surfaces 61, 62 are maintained in contact with the surface ofeccentric cams 27, 24, the web core spacing remains'constant. Springs53, 54 ensure that this contact will be maintained over a wide range ofdimensional changes in sideplates 14-17 of frame units 12 and 13. Thus,the expansion of portions of frame units 12 and 13 due to heating by thefusing station, or due to thermal variations from any cause, does notaffect the web-core spacing in the disclosed invention.

As has been made evident from the above description, the

invention disclosed herein enables a very simple and precise adjustmentof the web-core spacing in an electrostatic copier, which can beaccomplished very quickly and which does not require sophisticatedtechnical ability to perform. Moreover, when it is desired to change theoverall intensity of the visible image developed on the copier web, thismay be conveniently accomplished in a minimum of time by simplyloosening lock screw 65 of support member 22 and rotating knobs 25, 26in unison. For this purpose, the decorative housing for the copier maybe provided with a removable cover which, when removed, exposes knobs25, 26, eccentric cam 27, and lock screw 65. As is further evident fromthe above description, once the desired web-core spacing has been fixed,the invention provides an extremely simple and reliable mechanicalarrangement for maintaining this spacing constant independently ofthermal variations in the dimensions of the copier frame unit.

While the foregoing provides a full disclosure of the preferredembodiment of the invention, it is understood that variousmodifications, alternate constructions, and equivalents may be employedwithout departing from the true spirit and scope of the invention. Forexample, leaf springs or a single serpentine spring may be substitutedfor springs 53, 54 to provide a rearward thrust to developer magazine33. Also, other equivalent fastening devices for securing anchor bar 55to sideplates 16, 17 may be provided. Therefore, the above descriptionand illustrations should not be construed as limiting the scope of theinvention which is solely defined by the appended claims.

What is claimed is:

1. In an electrostatic copier having a main frame unit, axerographically sensitive member located in said main frame unit fordeveloping a latent electrostatic image, a second frame unit, and adeveloper unit carried by said second frame unit for rendering saidlatent electrostatic image visible, said developer unit having a brushmember spaced from said xerographically sensitive member for depositingtoner on the surface thereof, and a window for exposing a portion ofsaid brush member, the improvement comprising:

spacing means for adjusting the spacing between said brush member andsaid xerographically sensitive member along the width thereof, and

means coupled to said developer unit for coacting with said spacingmeans to maintain said spacing constant along the width of said brushmember and said xerographically sensitive member,

whereby said spacing is maintained constant independently of dimensionalchanges in said copier frame units.

2. The apparatus of claim 1 wherein said spacing means comprises a stopmember adjustably mounted on said main frame unit relative to a fixedpoint thereon for providing a reference abutment surface for saiddeveloper unit, and means for firmly anchoring said stop member to saidmain frame unit.

3. The apparatus of claim 2 wherein said stop member comprises arotatable eccentric cam having a threaded radial bore, and

said anchoring means comprises a shaft secured to said main frame unitand a lock screw engageable with said threaded bore and the surface ofsaid shaft to lock said cam thereto.

4. The apparatus of claim 1 wherein said spacing means comprises a shaftjournaled at a first end thereof in said main frame unit,

a first eccentric cam fixed to said shaft adjacent said first end forproviding a first reference abutment surface for said developer unit,

a support fixed to said main frame unit for rotatably supporting theother end of said shaft,

a second eccentric cam positioned on said shaft adjacent said other endfor providing a second reference abutment surface for said developerunit,

means for axially adjusting said first and second eccentric cams to apredetermined position, and

means for locking said first and second eccentric cams in saidpredetermined positions.

5. The apparatus of claim 4 wherein said adjusting means comprises afirst knob fixed to said shaft adjacent said other end and a second knobfixed to said second eccentric cam.

6. The apparatus of claim 5 wherein said support includes a tubularmember having a threaded radial bore, and

said locking means includes a first lock screw engageable with saidthreaded radial bore and the surface of said shaft for interlocking saidshaft and said tubular member.

7. The apparatus of claim 6 wherein said second eccentric cam has athreaded radial bore, and

said locking means further includes a second lock screw engageable withsaid threaded radial bore of said second cccentric cam and the surfaceof said shaft for locking said second eccentric cam thereto.

8. The apparatus of claim 1 wherein said maintaining means comprises ananchor bar fixed to said second frame unit, and spring means coupled tosaid anchor bar for urging said developer unit against said spacingmeans.

9. The apparatus of claim 8 wherein said spring means comprises firstand second spring members located adjacent opposite sides of the frontportion of said developer unit.

10. The apparatus of claim I wherein said maintaining means comprisesfirst and second channel members coupled to said frame unit for slidablysupporting said developer unit at opposite sides thereof,

a pair of guide members secured to and protruding frontwardly of saiddeveloper unit,

an anchor bar rigidly secured to said second frame unit forwardly ofsaid developer unit and slidably disposed on said guide members, and

a pair of spring members coupled to said anchor bar for urg ing saiddeveloper unit against said spacing means.

1. In an electrostatic copier having a main frame unit, axerographically sensitive member located in said main frame unit fordeveloping a latent electrostatic image, a second frame unit, and adeveloper unit carried by said second frame unit for rendering saidlatent electrostatic image visible, said developer unit having a brushmember spaced from said xerographically sensitive member for depositingtoner on the surface thereof, and a window for exposing a portion ofsaid brush member, the improvement comprising: spacing means foradjusting the spacing between said brush member and said xerographicallysensitive member along the width thereof, and means coupled to saiddeveloper unit for coacting with said spacing means to maintain saidspacing constant along the width of said brush member and saidxerographically sensitive member, whereby said spacing is maintainedconstant independently of dimensional changes in said copier frameunits.
 2. The apparatus of claim 1 wherein said spacing means comprisesa stop member adjustably mounted on said main frame unit relative to afixed point thereon for providing a reference abutment surface for saiddeveloper unit, and means for firmly anchoring said stop member to saidmain frame unit.
 3. The apparatus of claim 2 wherein said stop membercomprises a rotatable eccentric cam having a threaded radial bore, andsaid anchoring means comprises a shaft secured to said main frame unitand a lock screw engageable with said threaded bore and the surface ofsaid shaft to lock said cam thereto.
 4. The apparatus of claim 1 whereinsaid spacing means comprises a shaft journaled at a first end thereof insaid main frame unit, a first eccentric cam fixed to said shaft adjacentsaid first end for providing a first reference abutment surface for saiddeveloper unit, a support fixed to said main frame unit for rotatablysupporting the other end of said shaft, a second eccentric campositioned on said shaft adjacent said other end for providing a secondreference abutment surface for said developer unit, means for axiallyadjusting said first and second eccentric cams to a predeterminedposition, and means for locking said first and second eccentric cams insaid predetermined positions.
 5. The apparatus of claim 4 wherein saidadjusting means comprises a first knob fixed to said shaft adjacent saidother end and a second knob fixed to said second eccentric cam.
 6. Theapparatus of claim 5 wherein said support includes a tubular memberhaving a threaded radial bore, and said locking means includes a firstlock screw engageable with said threaded radial bore and the surface ofsaid shaft for interlocking said shaft and said tubular member.
 7. Theapparatus of claim 6 wherein said second eccentric cam has a threadedradial bore, and said locking means further includes a second lock screwengageable with said threaded radial bore of said second eccentric camand the surface of said shaft for locking said second eccentric camthereto.
 8. The apparatus of claim 1 wherein said maintaining meanscomprises an anchor bar fixed to said second frame unit, and springmeans coupled to said anchor bar for urging said developer unit againstsaid spacing means.
 9. The apparatus of claim 8 wherein said springmeans comprises first and second spring members located adjacentopposite sides of the front portion of said developer unit.
 10. Theapparatus of claim 1 wherein said maintaining means comprises first andsecond channel members coupled to said frame unit for slidablysupporting said developer unit at opposite sides thereof, a pair ofguide members secured to and protruding frontwardly of said developerunit, an anchor bar rigidly secured to said second frame unit forwardlyof said developer unit and slidably disposed on said guide members, anda pair of spring members coupled to said anchor bar for urging saiddeveloper unit against said spacing means.